Electrical communication system



Patented Nov. 29, 1949 un.irnosjxTATE s1 onerosi signments; to `Internationalif.Standard lElectrice Cinporation,` Ne'wfliirk,V N YL a@ corporationof:

Application February 1 In GreatBritain Manchf13g` 194251 10 Claims.

The present' invention; relates l to 1 electrical communication systemsA andaccor-dingf thereto.;` provides`r` a-l transmission` systemv in which the bandwidth of the tI'arisI-nittedfrequencies:is-mod;V ulatedin accordanceswith theamplitude ofthe intelligence for-sgnal wave -to be communicated;` The: resulting waveform may be transmittedf alongaline-or may be used. tov modulate` a carrier. Waver inknown manner: The modulated carrier.-.` may be transmitted in: any-known manner, for i example,V radio; cablei orf dielectric guides;L

Inone rsystemfaccording to the present inven:. tion` an amplitude modulation in accordance with l the intelligence or signal Wave to be communi` catedV Fis: set up .iriirthel harmonics fof ai; distorted sine Wave;` whilst.:V the amplitude., .l off. the ".fundas. mental,.frequencylof` the'isaid distortedesine .Wave is imaintained constant` In one` embodimentiiof 1 the :invention:A` assinei 1k Waver whose frequencyfis higher than z the highest.; modulation :..frequency component `of the i intelli.-L gence wave `to beftransmittedis amplitude modus. lated in accordance with the signal or intelligence f: wave` byv any l knownsmethoi.. This :emodulateds Waveformis .thenrpassed:throughv a .limiten circuitl in: such:.a;.way as 4tolmit the; amplitude offthega modulatedl Wave to; at ,.least that .voi 'the Lsmallest; amplitudesine waveproducedain: tha-modulation.; The resulting Waveform may thus varyrfromfatz, sine.;wave innonez-casetora 50% pulse,;with acentain,..harmcnc, contentsthatis, the number. of harmonics of .the fundamental frequency; oftthezi. sine: Wave; depending; on the lmodulation;:depth. This uWave .iorm..is;used..to..modulate=x a.; carrier.r` wavef-andsince. thisgmodulation; variesxin ampli. tudei.between.two fixed. values, namelygzero.,l andg. the*` amplitude of: the :fundamental sine tvvave,V the;Y carrier :canibe :modulated 'to 100%. Without irisk. ofwover modulating.'y

Inrxone` suitable form of receiving arrangement:- the modulated carrier.I isfsreceived. on a. receiver. which is capable ,oihandling-:thenecessary handL widthfandthe;detectedswave is limitedzin amplis-- tude'ifor noise reductionwand` passed through am. high passlter. Thislterxis'so `designeollthate` therfundamental frequencyy .of the detectediiwavec` is L greatly attenuated while the harmonics `r are allowedV toV pass :freely: These'fh'armonicsl may loefv eachy looked uponas auf carrier '(harmonic carv riers) l modulated in amplitude "by' the original; signal4 or` intelligenc'ef` wave: The output 4`o1"v the-zn, iilter` is passedx through'-A a rectifier` and then through: a' ilcvv.v pass .lter: whichI attenuates` the harmonici carrier frequencies but ,passes thef: intelligencefirequencies Theselatterf are ample edasnecessary and.passed. tothe vworker trans-.ff

lating device.

The invention .will'.beimoreffullydescribed `,with reference.; to.. the accompanying drawings: in.,v

1 which?V Fig.` 1.-.is..aschematic 4diagram of `a.transmitter...

forv carrying out .the invention',A

Fig, 2 showsthewaveform:atpoint,I I of Eig-.1;Y Fig. 3Jshowsth'e waveform at point.I3.of-Fig..1';.

Fig. '4 shows the waveform atpointl 5 ofligi 1 band transmitter. 15#4 In Fig.. 1 the. signalvoltage wave representing mon to'valves Viy andVav and thus across resi-st? ance '.IT will be, developed ,'tlfiesine .wave.from

Ipoints 3 andlVand thistwillibe .amplitude moduv.

on the gnd'ofvffrompoints 1| and 2. Thismodulated sine Waveis shown in Fig'.,2,. the hatched 30'limitingwcircuit` one form of [which may consist of diodes V3 and V4" and their associated network ofjresistances andondensers -asshovvn in Fig. 1. Po'sltive volts which' may bevaried `loy resistance` lfareapplied tdthe .cathode of Vzland are ad-E condenser, 2 I. pass..a11 positive .voltages applied to its anodein excessofthepreset voltage on the` 40V"Similarly lloy applyingthewaveform tothe cathparte. of:y thewaveform g in. Fig. 2 `is `bypassed the.wavefornnoripulsefdepends upon the ampli,-

Fig,V 5- is' `theschematic diagram of receiving... arrangements...fr ,cofoperation witna transmit-- l ter as in Fig. 1' or anyother modulated frequency *lated in. accordancelwitlith'e .Waveform imposed.,

"justed in such a manner that the diode V3 andf ,-throughl,.Vtancli. condenser,- 3.3;.: This `part. Whichf. is-removedxs shovvnihetween` theflines ,.21 and v29.1.l in ,.Fig.'; 2.' Thefresultinggwaveform is shown gin;` Fig;` and itiwillvbe observedthat .the slope off- 2 tudefioffthe:modulatingwave and ftheacomponent` harmonicifrequencies or .bandggwidth ofthe Awave`` formaoripulse dependsupon-.theslope oflthe lead#V4 ing-"and,` trailingf: edges of i' theflwaveform. This s' waveform-*may now@ ybe usedto :modulate a carrier.`

lirnwave'- inf.anwysknowntmannen Thea;envelope-off 3 the final modulated carrier waveform is shown in Fig. 4.

The circuit diagram of a receiving arrangement is shown in Fig. 5. The signal is primarily received by any known technique, care being taken that the circuits involved can handle the frequency bandwidths required which is limited by the modulation depth in the transmitter. The signal, from the detector of the radio receiver at the points 'l and 8 which is shown in Fig. 3 is fed into a limiter circuit one type of which is shown consisting of V5 and Vs, which are diodes, and their associated circuits. The principle of operation is exactly similar to the limiters in the transmitter (Fig. l) and V3 coincides with V5; V4 with V6; resistances I9 and 3| (Fig. 1) with resistances 31 and 39 (Fig. 5) respectively; and condensers 2| and 33 (Fig. l) with condensers 4l and 43 (Fig. 5) respectively. The purpose of this limiter is to reduce noise by limiting the noise components from the crests and troughs of the received pulses.

`The output from the limiter V5 and Vc is now passed through condenser to a high pass filter 4l. This filter is so designed as regards its cut off frequency that it heavily attenuates the fundamental frequency of the pulse train applied to it while allowing free passage to the harmonics in the pulse. The wave-form at the out put terminals 9 and i0 of the filter is thus a compleX carrier composed of the harmonics contained in the pulse and which bear the initial intelligence voltage Wave in the form of an amplitude modulation.

The output from the high pass lter il is fed through a diode Vv on resistance de to perform the necessary detection of this harmonic carrier and thence Via terminals l2 and lli to a low pass filter 5l. the cut off frequency is at the same frequency or slightly lower than that of the fundamental frequency of the wave-form at points l and 8 in ig. 5 and which is shown in Fig. 3. The output from this lter 5| at points I3 and lll is the voltage corresponding to the intelligence or signal wave which is transmitted and may be connected to a speaker or some such appliance for audibility, or other work device.

Whereas the more conventional systems of radio transmission and reception are subject to noise interference, this system as described gives a greater signal noise ratio due to the limiting circuits in the receiver and also to the filters which allow only part of the noise spectrum t0 pass.

A greater modulation depth in the radio frequency carrier may be obtained than with amplitude modulation systems since the amplitude of the pulses is constant. There is also the greater peak power transmission for a given valve than is normally associated with forms of pulse transmission.

Whilst only one specific embodiment of the invention has been described, others falling within the scope of the appended claims will occur to those skilled in the art. tain the inteiligence signals from the received modulated band-width signals, a damped oscillatory circuit may be employed and the received detected signals applied to shock excite the oscillatory circuit. The amplitude of the initial cycle of the oscillation produced depends upon the rate of change of strength of the exciting current with time, and thus since the slope .of the edges of the This latter is so arranged that .y

For example, to obdetected received wave-form or pulses vary in accordance with the amplitude of the initial intelligence or signal wave, if the detected received wave-form or pulses be applied to shock excite the damped oscillatory circuit, preferably tuned to the pulse repetition frequency, or the frequency of the detected wave-form, the output of said circuit will follow the amplitude variations of the initial signal wave. The output of the oscillatory circuit may then be applied directly to a translating device or other work device.

What is claimed is:

l. In an electrical communication system, means for producing electrical intelligence waves of varying amplitudes, means for modulating less than the amplitude of a sine wave whose frequency is higher than the highest modulation frequency component of the intelligence wave to be communicated, circuit means for limiting the amplitude of said modulated wave to at least that of the smallest amplitude sine wave produced in the modulation, and means for modulating a carrier wave in accordance with the wave-form produced by said circuit means.

2. In an electrical communication system, means for producing electrical intelligence waves of Varying amplitudes, means for producing a wave-form Varying from pure sine wave to a pulse with a predetermined harmonic content, and means for modulating said Wave-form in accordance with said amplitudes, the number of harmonics of the fundamental frequency of said sine wave depending on the depth of the modulation.

3. In an electrical communication system, means for producing electrical intelligence waves of varying amplitudes, means for modulating less than 100% the amplitude of a sine wave whose frequency is higher than the highest modulation frequency component of the intelligence wave to be communicated, circuit means for limiting the amplitude of said modulated wave to at least that of the smallest amplitude sine Wave produced in the modulation, means for modulating a carrier wave in accordance with the wave-form produced by said circuit means, whereby this modulation varies in amplitude between the two fixed values of Zero and the amplitude of the fundamental sine wave.

4. An electrical communication system for transmitting and receiving intelligence comprising means for generating signal Waves having a predetermined fundamental frequency, means for varying the time rate of change of said waves between two amplitude levels in accordance With the intelligence to be transmitted while maintaining the maximum amplitude and the fundamental frequency of said waves substantially constant, means for transmitting said distorted waves, means for receiving said distorted Waves and means for demfodulating said waves.

5. An electrical communication system for transmitting and receiving intelligence waves comprising means for generating signal waves having a predetermined frequency, means for varying the time rate of change of said waves between two fixed amplitude levels corresponding to the lowest amplitude intelligence waves, in accordance with the intelligence to be transmitted, means for generating a carrier wave, means for modulating said carrier waves by said distorted waves, means for transmitting said modulated carrier waves, means for receiving said modulated carrier waves, means for detecting said modulated carrier Wave and means for demodulating the output signals of said detecting means.

6. An electrical communication system for transmitting and receiving intelligence comprising a source of electrical waves whose amplitude vary with the intelligence being transmitted, a source of carrier frequency sine waves, means for amplitude modulating said carrier waves with said electrical waves to derive complex waves, means for varying the harmonic content of said complex waves vin accordance with said amplitudes While leaving the fundamentals and amplitude of said complex waves unmodulated comprising means for varying the time rate of change of said complex waves to change between two amplitude levels in accordance with said amplitudes, means for transmitting the modulated complex waves, means for receiving said modulated complex waves, means for detecting said modulated complex waves, and means for attenuating the fundamental frequency of the detected wave while freely passing the harmonics, means for deriving said intelligence from said harmonics.

7. In a communication system a source of modulating waves, a source of carrier waves, means for amplitude modulating said carrier waves with said modulating waves to obtain modulated waves, means for limiting said modulated waves to the amplitude corresponding to the lowest amplitude modulating wave to derive waves harmonically related to the frequency of the lowest amplitude modulating waves and amplitude modulated in accordance with the modulating waves, and unmodulated waves at the frequency of the lowest amplitude modulating waves, and means for transmitting said derived and said unmodulated waves.

8. An arrangement according to claim 7, wherein said modulating waves comprise sine waves and said means for limiting comprises means for limiting the amplitude of the modulated waves to the amplitude of the lowest amplitude sine waves.

9. A receiving system for carrier waves amplitude modulated in accordance with a source of modulating waves, said modulated waves comprising waves harmonically related to the frequency of the lowest amplitude modulating waves and amplitude modulated in accordance with the modulating waves, and unmodulated waves at the frequency of the lowest amplitude modulating Waves, comprising means for receiving said modulated carrier waves, a high pass i'llter, means for applying said received waves to said filter to attenuate the unmodulated waves while passing said waves harmonically related to the frequency of the lowest amplitude modulating waves, means for amplitude detecting the passed harmonically related waves, a low pass filter, means for applying said amplitude detected waves to said 10W pass filter to derive said modulating waves.

l0. An electrical communication system for transmitting and receiving intelligence comprising a source of modulating waves, a source of carrier frequency Waves, means for amplitude modulating said carrier waves with said modulating waves to obtain modulated waves, means for limiting said modulated waves to the amplitude corresponding to the lowest amplitude modulating waves to derive waves harmonically related to the frequency of the lowest amplitude modulating waves and amplitude modulated in accordance with the modulating waves, and unmodulated waves at the frequency of the lowest amplitude modulating waves, means for transmitting said derived and unmodulated Waves, means for receiving said transmitted waves, means for separating said unmodulated Waves from said waves harmonically related to the frequency of the lowest amplitude modulating Waves, means for amplitude detecting said harmonically related waves after separation, and means for processing said amplitude detected waves to derive said modulating waves.

PRAFULLA KUMAR CHATTERJEA. DERMOT MIN AMBROSE.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 1,564,627 Round Dec. 8, 1925 1,584,327 Schelleng May 11, 1926 1,655,543 Helsing Jan. 10, 1928 1,678,163 Peterson III July 24, 1928 1,699,570 Potter Jan. 22, 1929 1,876,793 Thompson Sept. 113, 1932 1,911,253 Washington May 30, 1933 1,971,383 Prinz I Aug. 28, 1934 2,061,734 Kell Nov. 24, 1936 2,085,011 Ditcham June 29, 1937 2,205,359 Jensen II June 18, 1940 2,230,243 Haffcke Feb. 4, 1941 2,257,282 Smith et al. Sept. 30, 1941 2,266,401 Reeves Dec. 16, 1941 2,279,659 Crosby Apr. 14, 1942 2,303,493 Purington Dec. 1, 1942 2,404,306 Luck July 16, 1946 2,416,329 Labin et a1. Feb. 25, 1947 

